1. Field of the Invention
The present invention relates to a microcomputer system, and more specifically to that capable of reducing power consumption.
2. Description of the Prior art
Referring to FIG. 6, prior practice of a microcomputer system is exemplified in the form of a block diagram.
As illustrated in the figure, designated at 1 is a microcomputer system such as a personal computer and controls, etc., which comprises a processor unit 5 (hereinafter, referred to as a microprocessing unit (MPU).) composed of a central processing unit (hereinafter, referred to as a CPU.) 2 and of a buffer 4 connected to the CPU2 through an internal bus 3, peripheral equipment composed of a ROM (read only memory) 7 as an external memory device connected to the buffer 4 through an external bus 6, of a RAM (random access memory) 8, and of a data input/output unit (hereinafter, referred to as an I/O unit.) such as a parallel port and a serial port, a block 12 connected to the MPU5, and a watch 13 connected to the external bus and including a counter, the MPU5 and the peripheral equipment 7 to 9 each comprising one-chip LSIS. The CPU2 drives the external bus 6 through the buffer 4 for reading a basic program stored in the ROM7, and writing and reading data and user programs into and out of the RAM8. Additionally, it inputs and outputs data into and from external equipment through the I/O unit 9.
The microcomputer system 1 must read out the programs and data stored in the ROM7 and the RAM8 for executing the programs through the CPU2. For this, an address of the ROM7 or the RAM8 in which such a program has been stored is outputted to the ROM7 or the RAM8 through the internal bus 3, buffer 4, and external bus 6. The ROM7 or RAM8 outputs the program or data stored therein at the foregoing address onto the external bus 6 which is in turn read into the CPU2 through the buffer 4 and the internal bus 3. Further, when the CPU2 executes any processing corresponding to the program or data and outputs data to the peripheral equipment 7 to 9, the data is outputted again through the internal bus 3, buffer 4, and external bus 6.
The prior microcomputer system constructed as described above must access the external bus 6 at all times to which the peripheral equipment 7 to 9 have been connected, consuming more power than required. Further, in order for it to operate as a system, it is needed to input/output data at all times so that it is impossible to turn off a power supply of the peripheral equipment 7 to 9 or reduce voltage as well as to restrict the consumed power of the entire system.